The PDE10A inhibitors can be used to raise levels of cAMP and/or cGMP within cells that express the PDE10A enzyme (or just PDE10A for short), especially neurons that comprise the basal ganglia, and PDE10A inhibitors would therefore be useful in treating a variety of associated neuropsychiatric conditions involving the basal ganglia such as neurological and psychiatric disorders, schizophrenia, bipolar disorder, obsessive compulsive disorder, and the like, and may have the benefit of avoiding side effects, which are associated with the current therapies on the market.
WO 08/020,302 (Pfizer Products Incorporated) discloses the use of heteroaromatic quinolinebased compounds that serve as PDE10A inhibitors. WO09/152,825 (Lundbeck A/S) provides phenylimidazole derivative compounds that are PDE10A enzyme inhibitors, and as such are useful to treat neurodegenerative and psychiatric disorders.
A difficulty in the development of compounds useful for the treatment of neurological and psychiatric disorders has been the lack of appropriate animal models, the limited accessibility to the brain for pharmacokinetic measurements and lack of adequate direct biomarkers relating to action on the target system. Therefore, more accurate models for performing pharmacokinetic and pharmacodynamic modelling are desired and may be used along with e.g. plasma exposures. It is therefore clear that compounds that may lead to a better pharmacokinetic and pharmacodynamic modelling are valuable.
Non-invasive, nuclear imaging techniques can be used to obtain basic and diagnostic information about the physiology and biochemistry of living subjects. In nuclear imaging technique procedures, isotopes are combined with or chemically reacted with other chemical compounds or pharmaceuticals to form radiolabelled compounds. These compounds, once administered to the living subject, can localize to e.g. specific organs, cellular receptors or enzymes. This property of radiopharmaceuticals allows nuclear imaging techniques the ability to produce images which reveal the distribution and concentration of the radiolabelled compound as a function of time.
Positron Emission Tomography (PET) is of particular interest for drug development because of its high sensitivity and ability to provide quantitative and kinetic data. To conduct a PET scan, a short-lived radioactive isotope is injected into the living subject, usually into blood circulation. The radioactive isotope is chemically incorporated into a biologically active molecule, in the case of the present invention the radioactive isotope is incorporated into a PDE10A inhibitor. The radioactive isotope undergoes positron emission decay which eventually leads to the production of annihilation (gamma) photons which are detected when they reach the scintillator in the scanning device. The PET technique therefore depends on radioactive isotopes which undergo positron emission decay. These radioisotopes include carbon-11 (also symbolized 11C or 11C), nitrogen-13 (also symbolized 13N or 13N), oxygen-15 (also symbolized 150 or 15O), and fluorine-18 (also symbolized 18F or 18F).
WO 2006/053785 (Glaxo Group Limited), WO 2006/075226 (Pfizer Products Inc.), WO 2009/033584 (Bayer Schering Pharma AG), and WO 2010/097367 (Janssen Pharmaceutica NV) disclose various radiolabelled compounds for positron emission tomography.
Celen et al. Neurolmage 2010, 52, Supplement 1, P. S15, Celen et al. The Journal of Nuclear Medicine 2010; 51: 1584-1591, and Tu et al. Nuclear Medicine and Biology 2010; 37: 509-516 disclose 18F and 11C labelled compounds for PET imaging of PDE10A enzymes in the brain.